Comparison of asexual blood-stage antigens of Plasmodium falciparum recognized by antibody reagents from nine laboratories.

Several laboratories have reported a large number of plasmodial antigens that may be implicated in the immune-mediated protection against the asexual blood stage of Plasmodium falciparum. In order to establish relationships between the antigens reported by different laboratories, a comparative testing of 37 antibody reagents was carried out at the Reference Laboratory for Malaria Antibodies and Antigens. Based on the results of the comparative testing, these antibodies were divided into seven groups according to similarities in the stage-specificity, the subcellular localization and the apparent molecular mass (M(r)) of the antigens they recognized.Twenty-two antibody reagents were grouped together on the basis that all gave a characteristic grape-pattern in indirect immunofluorescence (IIF) and precipitated a schizont/merozoite antigen of M(r) 190 000 to 205 000. Another group consisted of one antibody which reacted with a M(r) 90 000 protein expressed only in mature trophozoites and young schizonts. A third group consisted of three antibodies which reacted with all blood stages of the parasite and recognized a M(r) 36 000 protein. The fourth group contained one antibody which recognized a M(r) 14 000 protein and gave an IIF staining of schizonts. The fifth group consisted of an antiserum raised against a fusion protein. This antiserum reacted with schizont and ring-stage parasites and precipitated a M(r) 75 000 antigen. One rabbit antiserum raised against a different fusion protein and one monoclonal antibody (Mab) were put together in the sixth group on the basis that both gave a cytoplasmic IIF staining of schizonts and recognized a strain-specific, M(r) 250 000 antigen from one P. falciparum strain. A seventh group was made up of 8 antibodies on the basis that all gave a similar two-dot IIF staining pattern of segmented schizonts and free merozoites, although these antibodies recognized four different sets of antigens.These results were presented to a subcommittee of the Scientific Working Group on the Immunology of Malaria (SWG-IMMAL) during a workshop held at the reference laboratory. The P. falciparum proteins recognized by the antibody reagents used for this workshop represent only some of the different types of asexual blood-stage antigens that have been described in the literature..